Who the primary antagonist of the first Scooby-Doo live action movie turns out to be. (It's Scrappy Doo.)
Actually, every single scene featuring Scrappy qualifies. He's so obnoxious, annoying and over-the-top in this movie, but it's delivered with such supreme comedy timing that his parts are among the funniest in the movie.
The Scooby-Doo Show's "A Highland Fling With a Monstrous Thing" has a surreal gag where Shaggy literally runs into an old skeleton hanging from some chains. The skeleton swings and twitches on its chains to the point where, as Shaggy escapes in panic, it hops off and runs away, mirroring Shaggy's run. It's utterly nonsensical and strangely hilarious.
In the movie, Fred and Daphne swap bodies... and Fred seems very happy that he can touch Daphne's breasts now.
Also from the first live action movie, Shaggy telling Daphne why they "Don't do castles". Bonus for Scooby acting everything out behind him, and glancing over his shoulder after Shaggy mentions being followed.
Daphne: How many times has that actually happened?
Shaggy: Twelve. We're not gonna do it.
From the same film, there is a short clip from an "instructional video" on how college kids should act, which includes the following scenario as to What NOT to do after having someone bump into you and spill your drink:
Nice Guy: Oh! Sorry, bro!
Angry Guy (as he breaks the glass with one hand): I will CRUSH YOUR BONES INTO DUST!